Promo Video or not?

Hello,

I'm just wondering what people's experiences have been using promo videos in the app store. A lot of top games including games created with BB don't have app promotion video, but I did notice they have a promo video for Almost Impossible!. Maybe for a paid game its more important since you have to convince someone to part with money for a download.
So I would be greatful if you can help me clear my confusion by answering my question.

I'd appreciate any thoughts.
Thank you.